Beavers

People often disagree about the beaver. Some think
this master dam builder is the smartest thing in
fur pants, and they use such words as intelligent,
energetic, and helpful when speaking of it. Others
claim the paddle-tailed engineer is dumb, stubborn,
and destructive. A look at the beaver and its lifestyle
may show why opinions are so different.

No other creature besides humans controls its environment
as completely as the beaver – changing the surroundings
to meet its needs. And since water rules the beaver's
life, most of its efforts are aimed at making sure
it has a good supply.

One of the most distinctive parts of the beaver is its tail, which resembles a large, flat, scaly paddle.

The chubby beaver is slow and clumsy on land, waddling
along at the mercy of its predators. However, in water
it becomes a sleek, stream-lined swimmer that can travel
at five or six miles an hour. No wonder the beaver
chooses to surround itself with water and builds a
dam to make sure there's enough. Water provides protection
as well as an easy way to travel. As water backs up
behind the dam, it brings the beaver's food supply
within reach of the water. Raising the dam deepens
the water and spreads it to new food sources as old
ones are used.

Going back in time a million years or so, we discover
the beaver is the descendant of an 800-pound prehistoric
rodent. Adult beavers, which average between 30 and
60 pounds, may seem rather puny by comparison, but
they still rank as the second largest rodents in
the world, right behind the South American capybara
(kap-ah-BARE-ah). A record beaver found in 1921 weighed
110 pounds, and heavyweights that tip the scales
between 80 and 100 pounds still are caught occasionally.

The beaver has been described by some as a "furry
hunk of homeliness." This description may be close
to the truth, but from its big orange teeth to its
paddle-like tail, the beaver is designed for its aquatic
life and lumberjack activities.

Its fur coat, which looks messy when wet and ungroomed,
has an outer layer of long guard hairs that cover an
inner layer of wooly underfur. The underfur is so thick
and well oiled that water usually cannot reach the
skin beneath it. Those who have felt the beaver's fur
underwater describe it as smooth and slippery. This
slickness keeps water drag to a minimum as the animal
swims. The dark chestnut brown of its winter fur may
fade to a golden tan by spring. Fur colors range from almost black to reddish brown to
blond.

Frequent grooming is necessary to keep the fur tidy.
Each hind foot has a split or double toenail that serves
as a comb. Drawing the hairs through these double nails
removes excess water and straightens any tangles. Despite
its large size, the beaver can twist and bend to reach
every part of its wet fur with these toenail combs.
The toenails also serve as toothpicks to remove wood
splinters left between its teeth.

Once the fur is combed, it must be oiled. The beaver
does not always sit on its tail during the combing
process, but it cannot oil itself until it does. Sitting
back with its tail folded under its body exposes the
opening at the tail base in which the beaver's sex
organs and its large oil glands are located. Using
its front feet, the beaver reaches down, scoops up
the strong-smelling oil released from the glands, and
rubs it on the fur. The toenail combs then spread the
oil evenly through the fur. This grooming process takes
place right after the beaver leaves the water and requires
about ten or fifteen minutes to complete.

The yellowish oil, called castoreum, is also used by
the beaver to mark its territory. Using its front feet,
the beaver rakes together a mud patty, which often
contains wood chips and other debris, and places it
in a highly visible spot. It then soaks the patty with
castoreum. Researchers have found that this oil contains
at least forty-five chemical ingredients, and humans
have used the oil in making perfumes. The scented patty
reveals the sex of the beaver that made it and many
other messages only another beaver can understand.
It serves as a chemical communication system.

Unlike its northern relatives, the Texas beaver usually can move about during most of the winter season. Although the water's surface seldom freezes around its lodge, the southern beaver still gathers and stores a cache of twigs and branches under water for winter food.

Probably the most distinctive part of the beaver is
its tail, which looks like a large scaly paddle. The
adult's tail is about a foot long, six or seven inches
wide, and less than an inch thick. The base is covered
with the same type of fur as the body, but the flat,
scaly part of the tail has only a few short, bristly
hairs.

The tail serves as a prop on dry land, bracing the
beaver as it cuts down a tree and helping the beaver
sit up so it can use its front feet for various chores.
At any sign of danger the beaver slaps its flat tail
on the water's surface with a loud smack, creating
a big splash before it dives to safety. Some observers
believe that slapping the tail in water and on land
not only is a warning signal for fellow beavers, but
also may be a sign of anger or an attempt to frighten
away an approaching predator.

A downward thrust of the tail as the beaver submerges
helps push its body under. Once underwater, the tail
acts as a diving plane, determining the angle of descent.
It also serves as a rudder, keeping the beaver on a
straight course, especially when the animal is towing
a tree or large branch. Seldom, if ever, is the tail
used for actual swimming.

Large, webbed hind feet deliver the powerful strokes
that push the beaver through the water. The webbing
folds together ducklike as the foot is brought forward
and spreads wide for the backward thrust. If the beaver
is in no particular hurry, its back feet stroke at
the same time, sending it forward in a smooth glide.
As the forward movement slows, the feet stroke together
again. But when the beaver needs to turn on the speed,
it switches to alternate foot strokes. Since each foot
is six or seven inches long and spreads to a width
of about six inches, each individual kick produces
quite a bit of forward thrust.

To further streamline its shape in the water, the beaver
hugs its front legs to its chest. The front feet are
clenched into fists and serve as bumpers. These flexible
front feet can be used almost like hands. Even though
the beaver doesn't have thumbs, it has five fingers
that are able to pick up and grip objects with ease.

While the beaver is underwater, its heartbeat slows
so less oxygen is needed. An extra large liver and
big lungs make it possible for the beaver to store
air and oxygen-rich blood for long dives. Three minutes
is the beaver's usual time underwater, but it can stay
down for as long as fifteen minutes. It's not unusual
for the beaver to travel as far as half a mile underwater
before surfacing, especially if frightened.

American beaver

The beaver has several waterproofing devices that go
into operation as it submerges. Valves in the ears
and nostrils snap shut and membranes slide over the
eyes like goggles to protect them and increase their
underwater vision. Folds of skin meet tightly behind
the large front teeth to seal off the mouth. These
folds of skin also prevent splinters from entering
the mouth as the beaver chomps away on land or in the
water.

Speaking of chomping, another unmistakable feature
is the beaver's large, orange buckteeth. As with other
rodents, these front teeth grow continually and are
kept worn down by constant gnawing. The front surface
is very hard enamel that wears slowly. The backs are
of a softer material that wears faster. This unequal
wear gives the teeth a chisel-like edge, and the angle
the edges form makes it possible for the beaver to
sharpen them against each other. The sixteen molars
used to grind the beaver's woody food seldom show any
sign of wear.

Small twigs are fed into the mouth with the front feet,
nipped into small pieces by the front teeth, chewed
by the molars, and swallowed. When eating bark off
larger sticks, the beaver picks up a piece about a
foot long. One "hand" closes around it and
the other grips it between the little finger and the
other four. The stick is turned quickly and evenly
by the fingers and moved slowly sideways. The sharp
front teeth strip off the bark as you might eat corn
off a cob. When its mouth fills with bark, the beaver
pauses, chews, swallows, sharpens its teeth, and then
continues eating. Upon nearing the end, it holds the
stick against the "palm" of its "hand" so
the teeth can eat right up to the edge. The cleaned
stick is then tossed aside and another is picked up.
The discarded sticks have an almost threaded appearance
because of the grooves the teeth cut while removing
the bark from the turning stick. Later these cleaned
sticks will be used to reinforce the beaver's dam.

A beaver dam is a remarkable structure, but the builder's
reputation for engineering intelligence may be slightly
exaggerated. Researchers who have spent time studying
these dams say that persistence and hard work may be
more responsible for the finished product than any
so-called engineering skills. In many cases a dam that
would hold the same amount of water could have been
built with only a fraction of the work if it had been
placed either upstream or down-stream from the chosen
site. But whether the location seems ideal by human
standards or not, once the site has been selected,
the beaver stubbornly refuses to build elsewhere. Why
the beaver chooses one site over another has puzzled
people for years.

This untidy pile of sticks is a beaver dam. It is remarkably strong and leak-proof as long as a beaver is using it and keeping it repaired.

Beavers observers don't always agree on the way the
dam is started. One explanation for the different methods
observed may be that beavers are adaptable. Some claim
beavers cut down a tree so that it falls across a creek.
Logs and branches are then floated downstream to catch
in the fallen tree. Others say beavers cut down branches,
tow them to the middle of a stream, stick them in the
mud on the bottom, and add rocks and more mud to keep
them there. More branches and logs are added and, when
the structure is tall enough, the beavers begin building
from it toward the shore.

According to Swedish researcher Lars Wilsson, who spent
several years studying a beaver colony and experimenting
with its residents, dam building is an instinctive
action triggered by the sound of running water. He
discovered that when plenty of water is available,
beavers may live in an area for some time without starting
a dam. But if the water level drops low enough to ripple
between or over some rocks or debris, the sound of
the shallow, running water attracts the beavers and
triggers a building urge. His captive beaver tried
to build a dam in a bathtub full of water when a recording
of running water was played beside the tub.

In the wild his beavers pushed or carried mud and rocks
from the bottom of the stream to the low spot where
the sound was occurring naturally. The low spot was
built up with these materials until water no longer
flowed over the top. The only problem was the water
now flowed around either side of it, continuing to
make the sound. This, too, had to be stopped, so the
barrier was extended on each end. Grass, leaves, twigs,
and other such materials were used, along with more
rocks and mud.

There is no mistaking the presence of a beaver in the neighborhood. The distinctive work done by its powerful incisors gives it away. These front teeth, which grow continually throughout the beaver's life, can cut great chips from a tree and topple it to the ground, as shown here.

Eventually each end of the barrier reached land and
the structure could be called a dam. But this wasn't
the end of the work. As the water built up behind the
low barrier, it got deep enough to flow over the top
again. The beavers' solution was to add more material
and raise the height of the dam.

Whatever building material is available is used in
the construction of a dam. If you or I were adding
sticks or small trees, we probably would place them
lengthwise across the stream, but this is not the beavers'
way. They place each stick or limb parallel to the
flow of the water. When possible, the butt end is wedged
into the muddy bottom and points up-stream while the
top leans toward the dam. Small trees may be included,
but mud, grass, leaves, and twigs are used to fill
spaces between the larger pieces and stop leaks. Busy "hands" poke,
probe, and ram small sticks into place. Debris carried
downstream also catches in the dam and helps plug any
holes. A dam in good repair leaks very little.

A pair of beavers can build a dam across a small stream
in two or three days. Their untidy pile of wood may
not look too impressive when the dam is finished, but
don't sell them short. When the need arises, they are
able to build some fantastic structures.

In his book The World of the Beaver (J. B. Lippincott,
1964), Leonard Lee Rue III describes some large beaver
dams he has seen. The longest was about 800 feet and
the tallest stood about 8 feet above the water level
on the downstream side. Historical beaver dams included
one in Wisconsin in 1919 that was 12 feet high and
640 feet long. Another located in Wyoming in 1955 was
only 30 feet wide, but it stood 18 feet tall. Montana's
Jefferson River contained a beaver dam 2,140 feet long,
but the length record may be held by a 4,000-foot dam
in New Hampshire. The lake created by this record dam
contained forty beaver lodges.

A dam described in Lewis H. Morgan's book The
American Beaver and His Works (B. Franklin, 1970; reprint of
1868 edition) was more than 450 feet long and 18 feet
thick at the base; it contained probably 250 tons of
materials. Such a structure takes years of work and
generations of beavers to build and maintain.

In their place in the wilderness, beavers usually are
considered constructive animals. Their ponds hold water
for dry times, help control floods, and create attractive
environments for many different wildlife creatures.
However, when the beaver builds too close to human
neighbors, it usually is considered a nuisance or a
destructive animal. It's hard to consider the beaver's
needs when its pond floods your crops, roads, or pastures
or when its menu includes your trees and shrubbery.
When a beaver's dam conflicts with human interests
and attempts are made to remove it, we learn just how
stubborn or persistent beavers can be. The animals
will spend each night repairing or rebuilding a dam
that has been damaged or destroyed during the day,
and they will continue to do this indefinitely.

County road engineers often clash with beavers. Instead
of building a small bridge over a ditch or creek, the
engineers install a culvert pipe and then build the
road on top. This allows the water to continue to flow
under the road through the pipe. With just a little
work, the beaver can plug the pipe and back up water
that eventually will flood the new road.

Beaver den

Such culvert pipe battles have continued for years.
Each time the road workers remove the plug, the beavers
replace it. One county engineer claims the beavers
in the area have developed their ability to plug a
culvert pipe to a fine art. He is sure they must have
found some way to measure the inside diameter of the
pipe because they go out each time and cut one-inch
sticks about three-fourths the length of the pipe's
diameter. The sticks are placed around the inside of
the pipe with one end caught in the pipe corrugations.
At their other end, the sticks are overlapped and interwoven
toward the upstream direction. Pieces of brush and
other small debris are added to the upstream side and
the whole thing is plastered with mud. When the water
backs up, the pressure wedges the entire mass even
tighter.

The only practical solution to such a problem is destroying
the animals or live-trapping them and moving them to
a more suitable location. However, either solution
may last for only a season or two. By then a new pair
of beavers may move into the area, discover the pipe,
and decide it is perfect for their needs.

And where do these wandering beavers come from? They
are two-year-olds that have been driven from their
home lodges in the spring. Forced out on their own,
they must find mates and establish their own territories.

Let's assume that during his travels downstream, a
two-year-old male beaver meets a female beaver and
they decide to set up housekeeping. Together they choose
a suitable territory and, when necessary, start building
a dam. Once their water supply is assured, they build
a place to live. The home structure may be either a
lodge or a burrow.

Lodges, like dams, are built of mud, rocks, debris,
and wood. They may be completely or partially surrounded
by water and will have two or more underwater access
tunnels.

Burrows, most commonly used by southern beavers, are
built into the bank of the river, pond, or stream.
From underwater entrances the beavers tunnel into the
dirt and hollow out a living area above the waterline.
When the burrow comes close enough to the surface or
breaks through, a pile of interlacing sticks and branches
plastered with mud is constructed over the burrow site.
This gives added protection from land predators that
might try to dig into the burrow from the top. As time
passes and more surface material is added, the burrow
may begin to look more like a lodge.

The living chamber for the new couple may start out
small – one and a half to two feet tall and no
more than three feet or so in diameter. However, as
the family grows, the living area will be expanded.
Large families may construct two separate chambers
divided by a wall. Both chambers will have their own
en-trance tunnels, called plunge holes. Living chambers
three or more feet tall and six to ten feet in diameter
are common, and lodges eight to fourteen feet tall
and forty feet across at the base have been reported.

Each living chamber, regardless of its size, is divided
into two basic parts – one for eating and one
for sleeping. The main floor, which is built a few
inches above the water level, is used as a feeding
and grooming area. Any water brought in by the beaver's
fur drains off the elevated floor into the lower area
around the plunge holes. In the sleeping section, which
is built like a shelf a few inches above the main floor,
each beaver has its own soft bed of shredded wood.

In April or May of the following year the beaver pair
probably will become parents. As the time for birth
approaches, the female takes sole possession of the
burrow. The male takes up temporary residence elsewhere.
She prepares the bedchamber for the young by shredding
fresh bark into the softest of bedding. Her litter
may contain one to eight young, but four is the usual
number. The young, called kits, are born fully furred,
weigh about one and a half pounds, and have their eyes
open. They are miniatures of their parents, complete
with teeth. During the first two weeks they remain
in the burrow, feeding on a rich, yellow milk. By the
end of the first month they are ready to go with their
mother on swimming and feeding excursions. The male
moves back home when they are a couple of weeks old.

The young beavers stay with their parents in a family
group, sharing the lodge and helping to keep the family
dam in good repair. When the next litter is born the
following year, they are evicted with the father and
return to the home burrow when he does. However, in
two years, when the third litter arrives, they are
not allowed to return to the family lodge with the
father. They are forced to make their own way as their
parents did. Sometimes they are allowed to build their
own lodges and remain in the parents' area, but if
all the offspring from a beaver pair stayed, the colony
soon would strip the area of food. Forcing the two-year-olds
to find new territories extends the period of time
an area can support its resident beaver population.

Beavers live along many wooded rivers, lakes, and streams
in Texas, but their highest populations are found in
the northeastern part of the state. Legal trapping
efforts help keep their numbers under control.

Admired or despised (depending upon how close a neighbor
it happens to be), the beaver is an interesting member
of the wildlife community that always makes its presence
known.